The present invention generally relates to a high frequency heating arrangement, and more particularly, to a high frequency heating apparatus or microwave oven or the like, which is capable of automatizing cooking, for example, in thawing food articles, etc., by controlling functioning of the apparatus through estimation of a state of the food article based on detection of the state of electromagnetic waves within a heating chamber, and also to an electromagnetic wave detector to be used for such a high frequency heating apparatus.
Recently, there has been a stronger tendency toward automatization of cooking, for example, by automatic thawing of a food article through utilization of a high frequency heating apparatus.
In connection with the above, the conventional practice has been such that an operator inputs the weight of the food article by keys (referred to as "time-auto"), or the operator determines the weight of the food article through employment of a weight sensor which automatically detects the weight thereof, whereby a heating time is preliminarily set for each weight of the food article. Moreover, there has also been proposed another arrangement in which an antenna is disposed within a heating chamber to determine a proper heating time by utilizing the characteristic that the microwave power detected by the antenna without being absorbed by the food article varies inversely with the weight of the food article, for example, in Japanese Patent Laid-Open Publication Tokkaisho No. 52-2133, the construction of such an arrangement is briefly described hereinbelow with reference to FIG. 1.
In the known arrangement of FIG. 1, a frozen food article 2 is placed in a heating chamber 1, and electromagnetic waves i.e. microwaves represented by an arrow 4 are applied thereto from a microwave radiating portion 3. In this case, some part 5 of the microwaves 4 not absorbed by the food article 2 is received by an antenna 6 disposed within the heating chamber 1, and after being detected by a detecting circuit 7, fed to a control section 8. Since the amount of the microwaves as detected by the antenna 6 inversely varies with the weight of the food article 2, the weight of the food article 2 may be detected conversely, thus making it possible to set an optimum heating time.
However, the conventional detecting means as referred to above has various problems. In the first place, when a weight sensor is used, there has been such a disadvantage that the finished state tends to scatter due to the influence of the weight of a dish or container employed.
Meanwhile, in the case where the antenna is employed, the detection level tends to largely vary according to the antenna construction, the detection circuit construction, fitting accuracy therebetween the influence of any external electromagnetic field, etc., thus resulting in extremely unstable factors for determining a subsequent heating sequence and consequently, there is a problem in that an optimum finished state, can not be achieved.